This invention relates to a hand-held flashlight, and in particular, to a flashlight for use by a firefighter or the like which provides a beam of light that is capable of penetrating dense smoke or fog to a greater extent than flashlights that are presently in use.
Most flashlights that are presently used by firefighters, rescue personnel and others that are forced to deal with fire, utilize tungsten-halogen lamps that inherently produce light that is concentrated at wavelengths in the red portion of the visible spectrum. As a consequence, the output of the lamp appears yellow when compared to natural white light. The light therefore is not able to penetrate dense smoke to any great extent and the user typically is unable to identify objects such as doors, windows, stairways and the like at any appreciable distance.
A low wattage arc lamp has been developed by Welch Allyn, Inc. of Skaneateles Falls, N.Y. and is described in detail in U.S. Pat. No. 5,144,201 to Graham et al., the disclosure of which is incorporated herein by reference. Lamps of the type described in the noted patent have been built which are capable of producing almost natural white light with the lamp output being substantially uniform at wavelengths across the visible spectrum. A 21 watt lamp is now available in which the gap between the lamp electrodes is about 1.2 mm. The arc which is generated within this small gap approaches a point light source and exhibits high efficacy even at very low wattages. As will be explained below, this type of lamp when incorporated in a battery operated, hand-held flashlight is able to penetrate heavy smoke to enable the user to identify objects at distances unattainable by present day flashlights equipped with tungsten-halogen lamps.
A rechargeable metal arc flashlight is disclosed in U.S. Pat. No. 5,630,661 which employs a 24 watt arc lamp that is mounted inside a reflector for focusing the light output of the lamp upon a light diffusion screen which is fixed in position in front of the lamp. The screen uniformly distributes the light from the reflector over a wide area. Light from the screen is then passed through a collimating lens and a UV filter mounted in front of the lens element. The relative position of the lens with regard to the lamp may be varied to change the spot size of the flashlight. A ballast is mounted inside the flashlight housing which controls starting and sustaining the arc.
Although the flashlight disclosed in the '661 patent is an advancement in the art, the many optical elements mounted in front of the lamp reduces the power output of the lamp and lessens the device's ability to focus the output of the lamp into a concentrated spot. In addition, the flashlight lacks a number of safety features that are essential when dealing with hazardous situations. Some of these include the ability to restrike the lamp arc in the event it is extinguished while involved in an emergency. As is well known, if the arc is restruck too soon after it has been extinguished, the starting procedure will be adversely impacted and a rapid restart cannot be thereafter initiated. As a result, a person who is involved in dense smoke or the like can well find himself or herself unable to restart the arc lamp when it is most needed.
Other information relating to safety and operability of the lamp are also not found in prior art flashlights. This includes the amount of on-time experienced by the lamp which, of course, goes to the expected life of the lamp. Here again, a flashlight having a dying lamp is of little use to a person who is involved in an emergency situation. In the case of smoke, a lamp that might be still functional under normal usage can undergo spatial changes that will adversely effect its ability to penetrate dense smoke. Similarly, the condition of the battery must also be monitored to insure that sufficient battery life is available to survive an emergency.